In related art, in order to perfoun grinding for removing scales such as foundry sand adhering to a surface or rust formed on a surface of a base material after casting with respect to a casting, a blasting treatment has been performed to project hard particles onto the casting. The grinding of casting is often performed, using a shot media having iron as a main constituent (for example, Patent Literature 1).
In the operation of the blast device, the cycle of “projection→recovery→selection→projection” of the shot media is repeated. In this way, the shot media is repeatedly projected toward the workpiece. When the shot media collides with the workpiece, crushing or abrasion occurs in the shot media, and the shot media finally has the size incapable of being reused. For this reason, the shot media is required to have both of performances such as a prevention of crushing or abrasion in the shot media at the time of blasting treatment (long life expectancy), and a high grinding capability (high hardness).